The human T-cell leukemia viruses (HTLV) represent a family of T-cell retroviruses with three known members. HTLV type I (HTLV-I) has transforming activity in vitro and is etiologically linked to adult T-cell leukemia, which is known to be endemic in several parts of the world. HTLV-II is another retrovirus having transforming capacity in vitro, and has been isolated from a patient with a T-cell variant of hairy cell leukemia. HTLV-III, which has also been called lymphadenopathy-associated virus and is now known as the human immunodeficiency virus (HIV). is lytic for certain kinds of T cells and has been linked to the etiology of acquired immunodeficiency syndrome (AIDS). Unlike the HTLV-I and -II viruses. HTLV-III is not known to have in vitro transforming activity.
A monoclonal antibody (Mab) reactive against HTLV-I, has been reported (Matsushita). The antibody, designated 0.5.alpha., is an IgG.sub.1 Mab which binds to the cell membrane of T-cells infected with HTLV-I, causing cell lysis in the presence of complement. Electroblot studies indicate that the Mab reacts with the major envelop protein of HTLV-I (Matsushita). This protein, designated gp46, is the outer membrane component of the env gene product. A proviral HTLV-I genome has been isolated and sequenced in its entirety (Seiki). Using a competitive inhibition binding assay, it was observed that 15 out of 15 patients with adult T-cell leukemia had antibodies that blocked the binding of the Mab to disrupted HTLV-I virions (Matsushita). The antibody does not appear to bind to either the HTLV-II or HTLV-III virions or to infected cells.
Although the above-discussed studies indicate the possibility of using an anti-HTLV-I antibody for diagnosing HTLV-I infection, this approach has two major drawbacks. First, the assay system is relatively laborious, requiring both a source of HTLV-I virions, infected cells, or fractionated gp46 protein, and anti-HTLV-I Mabs combined into a competitive binding assay format. Secondly, whole virions, or even fractionated proteins thereof, are likely to react with more than one epitope-specific anti-HTLV-I antibody, thereby decreasing both the sensitivity and specificity of the test.